1. Field of the Invention
The present invention relates to a frame structure for flexibly supporting heterogeneous modes and time division duplexing (TDD)/frequency division duplexing (FDD) modes, and a method for transmitting and receiving signals using the same.
2. Discussion of the Related Art
In order to maximize the efficiency of limited radio resources in a broadband communication system, methods for efficiently transmitting/receiving signals in space, time, and frequency domains and utilization methods therefore have been proposed. A multicarrier-based orthogonal frequency division multiplexing (OFDM) scheme reduces the complexity of a receiver under frequency selective fading environments of a broadband channel, and increases spectral efficiency using different channel characteristics of subcarriers through selective scheduling in the frequency domain. In addition, the OFDM scheme can be extended to orthogonal frequency division multiple access (OFDMA) by allocating different subcarriers to multiple users, thereby increasing the efficiency of radio resources in the frequency domain.
As to wireless metropolitan area network (MAN)-OFDMA standard applying OFDMA, IEEE 802.16-2004, IEEE 802.16e-2005 amendment (hereinafter, referred to as ‘IEEE 802.16e’), etc. have been completed.
FIG. 1 illustrates a logical frame structure of an IEEE 802.16e system.
The logical frame structure of the IEEE 802.16e system includes a control signal part of a preamble 101, a frame control header (FCH) 102, a downlink (DL)-MAP 103, and an uplink (UL)-MAP 104 and includes data bursts. Data transmission of each user is defined by different subcarrier allocation schemes (e.g., partial usage of subchannel (PUSC), (optional)-full usage of subchannel ((O)-FUSC), tile usage of subchannel (TUSC), adaptive modulation and coding (AMC), etc.) according to a subchannel configuration method. Various permutation zones may be constructed in one frame.
A frame of the IEEE 802.16e system as illustrated in FIG. 1 is necessary to receive control information of the preamble 101, FCH 102, DL-MAP 103, and UL-MAP 104. A role of each field is as follows.                Preamble 101; synchronization, channel estimation, cell identifier (ID) acquisition, etc.        FCH 102: Provision of channel allocation information and channel code information, related to the DL-MAP 103.        DL-MAP 103 and UL-MAP 104: Provision of channel allocation information of data bursts in uplink (UL) and downlink (DL).        
The logical frame structure except for the preamble 101 among the above-described control fields may be variously constructed according to selected subcarrier allocation schemes (e.g., PUSC, (O)-FUSC, TUSC, AMC, etc.) in consideration of a frequency diversity gain, a scheduling gain, pilot overhead, or ease of application of multiple/adaptive antenna.
FIG. 2 illustrates a configuration of various permutation zones in an IEEE 802.116e system.
A proper subchannel allocation scheme is established in consideration of a frequency diversity gain, a scheduling gain, pilot overhead, or ease of application of multiple/adaptive antenna. This may be understood that various permutation zones are present as illustrated in FIG. 2 through a zone switch information element (IE) in a MAP.
The configuration of a preamble, an FCH, and a DL-MAP is indispensable in each frame as illustrated in FIG. 2 and thus a receiver can accurately acquire data or control information within the frame.
The conventional IEEE 802.16e frame structure as described above constructs DL and UL sub-frames in a 5 msec-frame structure to support TDD and constructs different subchannelization by time division multiplexing (TDM).
However, in order to extend a conventional TDD frame structure to a structure for supporting DL/UL paired spectrum such as FDD, a structure which is easy to apply an inherent performance enhancement technique in FDD should be designed. Specifically, in FDD, a sub-frame configuration is demanded which is a shorter unit than in TDD and is defined as a transmission Lime interval (TTI). Moreover, it is possible to design a basic unit transmitting the same modulation and coding scheme (MCS) level.
The TTI configuration of a short length of 5 msec or less may lead to reduction in a hybrid automatic repeat request (HARQ) latency and a channel quality indicator (CQI) latency in FDD. The reduction in HARQ latency and CQI latency increases spectral efficiency and transmission capacity. Further, frequency-selective scheduling, multi-user diversity, a closed-loop multiple-input multiple-output (MIMO) gain, etc. can be favorably obtained. Accordingly, a frame structure design suitable for TDD and FDD is demanded and proposal for a frame structure which can support commonality and conventional modes is needed.